[Toybox] TOYFLAG_ARGFAIL

[enh]

according to the coreutils docs, chroot/env/nice/nohup all have the
same "125 for command errors" behavior. that makes sense to me, and my
OCD wants to send you the patch, but i don't know whether that
conflicts with your dislike of adding stuff no-one's asked for.

timeout and grep are special in that we know people do check their
exit status, so i'm not sure whether we have precedent yet for this
behavior in general.

(as best i can tell, there aren't actually that many more such cases.
su does 125, runcon probably ought to but doesn't. cmp/diff/sort are
like grep with 2. ls and expr are both [but differently] weird. that
seems to be it?)